1. Technical Field
The present disclosure relates to spinal fixation and, more particularly, to anterior brackets for providing support and stabilization to the spinal column and for inhibiting expulsion of an interbody implant disposed within the intervertebral space.
2. Background of Related Art
The human spinal column is a complex system of bones and connective tissues that provides support for the human body and protection for the spinal cord and nerves. The adult spine is comprised of an upper and lower portion. The upper portion contains 24 discrete bones, which are subdivided into three areas including 7 cervical vertebrae, 12 thoracic vertebrae, and 5 lumbar vertebrae. The lower portion is comprised of the sacral and coccygeal bones. The vertebrae, or vertebral bodies, progressively increase in size from the upper portion downwards to the lower portion.
An intervertebral disc along with two posterior facet joints cushions and dampens the various translational and rotational forces exerted upon the spinal column. The intervertebral discs are spacers located between adjacent vertebral bodies, while the facets provide stability at the posterior portions of adjacent vertebrae.
The spine is a flexible structure capable of a large range of motion. There are various disorders, diseases and types of injury, however, which restrict the range of motion of the spine or interfere with important elements of the nervous system. These include, but are not limited to, scoliosis, kyphosis, excessive lordosis, spondylolisthesis, slipped or ruptured discs, degenerative disc disease, vertebral body fracture, and tumors. Persons suffering from any of the above conditions may experience extreme or debilitating pain and oftentimes experience diminished nerve function.
Spinal fixation apparatuses are widely employed in surgical processes for correcting spinal injuries and diseases. When an intervertebral disc has degenerated to the point of requiring removal, there are a variety of interbody implants that are utilized to take the place of the disc such as PEEK interbody spacers, metal cages and cadaver and human bone implants. In order to facilitate stabilization of these interbody implants, additional implants are commonly employed. For example, longitudinally linked rods may be secured to coupling elements which, in turn, are secured to bone by spinal bone fixation fasteners, e.g., pedicle screws, hooks, etc.
As an alternative to using rods, plate and screw systems may be employed to stabilize and secure the anterior or lateral portion of the spine. In one approach, a fusion implant is placed between the vertebrae and a substantially flat plate is secured across the intervertebral space, with the plate secured to the face of each adjacent vertebral body with screw screwed into cortical bone. This approach maximizes the fusion graft material that can be placed between the vertebrae, and maximizes the surface area contact between the fusion implant and the adjacent vertebra. In addition, the placement of the fusion implant is independent of the position of the plate. More recently, structures have been proposed to try to combine the plate and implant into a single implant. See, for example, Moskowitz U.S. Patent Application Publication No. 2008/0177307; Mathieu U.S. Pat. No. 7,232,464, Bray U.S. Pat. No. 6,984,234 and Fraser U.S. Pat. Nos. 6,432,106 and 7,112,222. In general, these proposed structures secure the fusion implant to a screw receiving structure, such that the screw receiving structure extends into the intervertebral space. These structures can reduce the available space for the fusion implant and can require a specific fusion implant that is designed to be mated with the screw receiving structure. Also, most such structures position the screw receiving holes such that the screws extend at a trajectory to engage the vertebral end plates, not the cortical bone of the vertebral bodies. Fraser includes caudal and cranial screw tabs for mounting the screws to extend into the face of the vertebral bodies, but requires that the screw receiving structure be attached to the fusion implant, thereby limiting flexibility of placement of the fusion implant. U.S. Patent Application Publication No. 2008/0312699 to Johnson et al. discloses a system including an intervertebral spacer for positioning between two vertebrae of a patient, and a plate for positioning within the intervertebral space and adjacent to the spacer for inhibiting the spacer from backing out of the intervertebral space. Johnson does not show his plate attached to the fusion implant, but he does show his plate wholly contained within the disc space, which reduces the available space to receive the fusion implant. Johnson's screws also extend into the end plates of the vertebral bodies within the disc space.